Function Of Experimental Conditions Research Articles

Electrospray Mass Spectrometric Detection of Products and Short-Lived Intermediates in Aqueous Aerosol Microdroplets Exposed to a Reactive Gas

The intermediates ISO3- (m/z=207) and IS2O3- (m/z=239) generated in aqueous (NaI/Na2S2O3) microdroplets traversing dilute O3 gas plumes are detected via online electrospray mass spectrometry within approximately 1 ms, and their stabilities gauged by collisionally induced dissociation. The simultaneous detection of anionic reactants and the S2O62-, HSO4-, IO3-, and I3- products as a function of experimental conditions provides evidence of genuinely interfacial reaction kinetics. Although O3(aq) reacts about 3 times faster with I- than with S2O32- in bulk solution, only S2O32- is significantly depleted in the interfacial layers of [I-]/[S2O32-]=10 microdroplets below [O3(g)] approximately 50 ppm.

Gas-Phase Ionization/Desolvation Processes and Their Effect on Protein Charge State Distribution under Matrix-Assisted Laser Desorption/Ionization Conditions

The charge state distribution of proteins was studied as a function of experimental conditions, to improve the understanding of the matrix-assisted laser desorption/ionization (MALDI) mechanisms. The relative abundances of the multiply-charged ions appear to be a function of the matrix chosen, the laser fluence and the matrix-to-analyte molar ratio. A correlation is found between the matrix proton affinity and the yield of singly- versus multiply-charged ions. These results are in good agreement with a model in which gas-phase intracluster reactions play a significant role in analyte ion formation. A new model for endothermic desolvation processes in ultraviolet/MALDI is presented and discussed. It is based upon the existence of highly-charged precursor clusters and, complementary to the ion survivor model of Karas et al., assumes that two energy-dependent processes exist: (i) a soft desolvation involving consecutive losses of neutral matrix molecules, leading to a multiply-charged analyte and (ii) hard desolvation leading to a low charge state analyte, by consecutive losses of charged matrix molecules. These desolvations pathways are discussed in terms of kinetically limited processes. The efficiency of the two competitive desolvation processes seems related to the internal energy carried away by clusters during ablation.

Non-parametric detection of temporal order across pairwise measurements of time delays

Neuronal synchronization is often associated with small time delays, and these delays can change as a function of stimulus properties. Investigation of time delays can be cumbersome if the activity of a large number of neurons is recorded simultaneously and neuronal synchronization is measured in a pairwise manner (such as the cross-correlation histograms) because the number of pairwise measurements increases quadratically. Here, a non-parametric statistical test is proposed with which one can investigate (i) the consistency of the delays across a large number of pairwise measurements and (ii) the consistency of the changes in the time delays as a function of experimental conditions. The test can be classified as non-parametric because it takes into account only the directions of the delays and thus, does not make assumptions about the distributions and the variances of the measurement errors.

Responses to the Stigmatized: Disjunctions in Affect, Cognitions, and Behavior

This study examined affective, cognitive, and behavioral responses to members of a stigmatized group – homosexual men. Male participants were placed in a situation in which they anticipated interacting with a gray or a non‐stigmatized conversation partner. The topic of the impending conversation was either potentially threatening or non‐threatening. Participants in the gay conversation partner condition sat either farther away from the conversation partner (in the threat condition) or closer to the conversation partner (in the no‐threat condition) than they did from non‐stigmatized conversation partners. There were no differences in attitudes toward the conversation partner as a function of experimental condition. The results were interpreted in terms of predictions based on ambivalence‐amplification theory, aversive racism theory, and the integrated threat theory.

Adaptable method for estimation of parameters describing bacteria transport through porous media from column effluent data: Optimization based on data quality and quantity

Bacterial transport through porous media is often modeled using the colloid filtration theory with a Langmuirian blocking function (CFT-LB), with experimentally derived transport parameters being the collision efficiency, the blocking parameter, and the clean-bed breakthrough concentration. Research trends are moving towards comparing small variations in these parameters as a function of experimental conditions, and the objective of this study was to determine impact of experimental design, including number of data points and experimental duration, on the suitability of the CFT-LB model to provide sufficient resolution to permit these comparisons. The results indicate that while the CFT-LB model captures the general trends in bacterial transport data, there are cases where the CFT-LB model cannot replicate the details in the column effluent curves, and this results in the estimated transport parameters varying as a function of the experimental duration. Impacts of these variations on interpretation of the transport parameters are discussed, and a recommended procedure is provided when applying the CFT-LB model to column effluent data. Ultimately, when the CFT-LB model is used to estimate bacterial transport parameters, the process should be completely transparent, allowing the general reader to know exactly how the transport parameters were obtained from the experimental data.

Effect of fretting amplitude and frequency on the fretting corrosion behaviour of tin plated contacts

The fretting corrosion behaviour of tin plated copper alloy contacts at 3, 10 and 20 Hz and at two different track lengths (fretting amplitude) of ±5 and ±25 μm is studied. The change in contact resistance as a function of fretting cycles, surface profile of the contact zone, extent of fretting damage, extent of oxidation and elemental distribution across the contact zone were used to assess the fretting corrosion behaviour. The time to reach a threshold value of contact resistance of 0.1 Ω is found to be early for the track length of ±5 μm compared to that of ±25 μm, at all the three frequencies. For a given track length, this threshold value reaches early at 20 Hz. The roughness and the nature of surface profile suggest considerable amount of oxidation have occurred at the track length of ±25 μm compared to that of ±5 μm. The surface morphology of the fretted zone reveals severe damage of the contact zone for samples with a track length of ±25 μm at all the three frequencies. A pictorial model is proposed to describe the evolution of change in area of the contact zone. Based on the length and width of the contact zone, the fretted area is calculated. The change is fretted area as a function fretting frequency and track length is analyzed. Delamination wear is found to be operative at both track lengths and at all three frequencies. EDX line scanning also indicates higher levels of oxidation at the track length of ±25 μm compared to that of ±5 μm. The variation in the atomic ratios of tin, copper and oxygen of the oxide debris present at the centre and edges of the fretted zone is plotted as an area plot as a function of experimental conditions. The debris is predominantly oxides of copper for the track length of ±25 μm whereas they are mostly oxides of tin for the track length of ±5 μm at all the three frequencies. The narrow and deep surface profile, lower Ra values, overlapping of the tin and copper lines in the EDX line scan and the predominance of oxides of tin support the view that the chances of accumulation of wear debris at the contact zone is very high at the track length of ±5 μm. The study concludes that tin plated contacts could encounter an early failure even at shorter track lengths of ±5 μm, if there is sufficient accumulation of the wear debris at the contact zone.

An artificial neural network model for toughness properties in microalloyed steel in consideration of industrial production conditions

The mechanical properties of an API X65 microalloyed steel were investigated with industrial thermomechanical experiments. The many parameters of processes obtained during production on the plant were systematically changed to optimise the strength and toughness properties. Among these parameters, parameters taking part in secondary metallurgy, such as used collemanite amount for slag formation, or stirring time for reducing of the non-metallic inclusions, which are not viguriously investigated in general, are included in the modelling. The optimised parameters were used for the production of the API X65 steel. However, it is not easy to determine as to what parameters under which conditions influence the toughness properties of the material. Therefore, in this study, a generalised regression neural network was developed to predict the impact energy as a function of experimental conditions. The predicted values of the impact energy using the neural network are found to be in good agreement with the actual values from the experiments.

The prediction of mechanical behavior for steel wires and cord materials using neural networks

The tensile strength of the steel wire material is required to be sufficiently high for better performance. Steel with a high cleanness will prevent problems during drawing and the heat treatment. The studies show that among many defects the most important ones are the non-metallic inclusions and undesirable phases encountered during improper heat treatment. Especially different non-metallic inclusions will play an important role during crack propagation due to their weak matrix bond. In this study typical wire and cord failures due to non-metallic inclusions are examined. A generalized regression neural network was developed to predict the tensile strength as a function of experimental conditions. The predicted values of the tensile strength estimated by neural network are found to be in good agreement with the actual values from the experiments.

A CRDS approach to gas phase equilibrium constants: the case of N 2O 4 ↔ 2NO 2 at 283 K

We report a general technique for determining the gas phase equilibrium constant, K P, of the A ↔ 2C system using cavity ringdown spectroscopy (CRDS). Working at a constant temperature, the absorption of one of the equilibrium species is measured at two different total pressures. K P is determined from the total pressures of the equilibrium mixture and the ratio of the absorptions. Theoretical limits on sensitivity of this technique are described as a function of experimental conditions. We present results from the reaction N 2O 4 ↔ 2NO 2 measured at T = 283 K. K P measured in this experiment, 21 (±5) Torr, is found to be lower than that recommended by the NASA Panel for Data Evaluation, 32 Torr. [S.P. Sander, A.R. Ravishankara, D.M. Golden, C.E. Kolb, M.J. Kurylo, R.E. Huie, V.L. Orkin, M.J. Molina, G.K. Moortgat, B.J. Finlayson-Pitts, Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies. Evaluation No. 14; Jet Propulsion Laboratory, Pasadena, CA, 2003].

Differences in motor recruitment and resulting kinematics between low back pain patients and asymptomatic participants during lifting exertions

Background. Low back disorders are a prevalent problem in society today and may lead to chronic debilitating low back pain. Developing our understanding of temporal muscle and kinematic patterns during manual material handling tasks may provide insight for preventing the cascading series of events leading to chronic low back pain. Methods. Sixty-two low back pain patients and 61 asymptomatic participants performed a variety of lifting exertions that varied in lift origin horizontal and vertical distance, lift asymmetry, and weight. Electromyographic activity of 10 trunk muscles as well as trunk and pelvic kinematics was recorded during each exertion. Differences in muscle activation and kinematic parameters were compared between low back pain patients and asymptomatic participants as a function of experimental conditions. Findings. Both the left and right erector spinae activated significantly earlier and were on significantly longer in low back pain patients compared to asymptomatic participants. The horizontal and vertical location of the lift influenced the EMG and kinematic differences between the low back pain patients and asymptomatic participants. Interpretation. These finding indicate that low back pain patients would be exposed to increase muscle activity resulting in higher spine loads for a greater length of time compared to asymptomatic participants. The longer exposure time to increased spine load may lead to greater risk of future low back injury and cascading events leading to debilitating low back pain. The longer muscle activation time suggests that low back pain patients have changed their motor program from an open to a closed loop system.

Congruent vaporization properties as a tool for critical assessment of thermodynamic data: The case of gaseous molecules in the La–O and Y–O systems

In the first part of this contribution, definitions of congruent or azeotropic vaporizations are given as a function of experimental conditions. Then, we show how to calculate these vaporization states by using thermodynamic software. Experimental aspects of congruent vaporizations are analysed in relation to chemical interactions between the sample and the container that change the original chemical system of the sample into a system of higher order for the analysis of congruent behaviours. In experimental determinations, three points must be checked: the partial vapour pressure ratios must be constant for all temperatures; the chemical nature of the sample must be unchanged and controlled after the experiments; and thermodynamic data derived from the experiments must lead to the calculation of the same congruent vaporization conditions. The concept of congruent vaporization can be used to assess thermodynamic data. For example, Y 2O 3 is observed experimentally to vaporize at high temperature according to the main reaction Y 2O 3(s)→2YO(g)+O(g). From thermodynamic databases, the calculated main reaction is Y 2O 3(g)→YO(g)+YO 2(g), and we conclude that the tabulated thermodynamic data for the species YO 2 are erroneous. The same conclusion is reached for the La 2O 3 compound and the LaO 2 gaseous molecule.

On the copper oxide neutral cluster distribution in the gas phase: detection through 355 nm and 193 nm multiphoton and 118 nm single photon ionization.

The distribution of neutral copper oxide clusters in the gas phase created by laser ablation is detected and characterized through time-of-flight mass spectroscopy (TOFMS). The neutral copper oxide clusters are ionized by two different approaches: Multiphoton absorption of 355 and 193 nm radiation; and single photon absorption of 118 nm radiation. Based on the observed cluster patterns as a function of experimental conditions (e.g., copper oxide or metal sample, ablation laser power, expansion gas, etc.) and on the width of the TOFMS features, one can uncover the true neutral cluster distribution of CumOn species following laser ablation of the sample. Ablation of a metal sample generates only small neutral CumOn clusters for m less, similar 4 and n approximately 1, 2. Ablation of copper oxide samples generates neutral clusters of the form CumOm (m < or = 4) and CumO(m-1) (m > 4). These clusters are directly detected without fragmentation using single photon, photoionization with 118 nm laser radiation. Using 355 and 193 nm multiphoton ionization, the observed cluster ions are mostly of the form Cu2mOm+ for 4 < or = m < or = 10 (193 nm ionization) and CumO1,2 (355 nm ionization) for copper oxide samples. Neutral cluster fragmentation due to multiphoton processes seems mainly to be of the form CumO(m,m-1) --> CumO(m/2,m/2+1). Neutral cluster growth mechanisms are discussed based on the cluster yield from different samples (e.g., Cu metal, CuO powder, and Cu2O powder).

The use of TG-FTIR technique for the assessment of hydrogen bromide emissions in the combustion of BFRs

The TG-FTIR technique was used in the present study to investigate the thermal degradation behaviour of materials containing brominated flame retardants under fire conditions. Time-temperature profiles and oxygen concentrations typical of selected fire scenarios were reproduced in the thermogravimetric analyzer, while the characterization of the gaseous products generated was performed by the simultaneous FTIR analysis. FTIR analysis combined with the use of specific calibration procedures allowed the quantitative estimation of the gaseous products evolved as a function of experimental conditions. The results obtained allowed the straightforward assessment and the comparison of the quantities of hydrogen bromide formed in the oxidation and thermal degradation of pure brominated flame retardants and of flame retarded materials of industrial interest. Hydrogen bromide yields resulted dependent on the experimental conditions used, such as oxygen concentration and heating rate. Although TG-FTIR experiments only provide a representation of the actual heterogeneous combustion products in real fire conditions, the coupled TG-FTIR technique proved to be a straightforward experimental methodology allowing one to obtain reference data on the nature and quantities of the macropollutants generated in a fire.

Entropy evaluation using the kinetic method: is it feasible?

The kinetic method is one of the most widely used experimental techniques for the measurement of thermochemical parameters by mass spectrometry. Recently it has been realized that it can also be used to determine reaction entropies, but the validity of this approach has not been established. This Perspective evaluates kinetic method plots in cases where there is a significant entropy difference between the competing fragmentation channels (i.e. between sample and reference compounds in the dissociating cluster ion). The concept underlying this study is to calculate mass spectra theoretically, based on known thermochemical parameters and as a function of experimental conditions. This can be done accurately using the RRKM-based MassKinetics software. The resulting mass spectra are then interpreted by the kinetic method, yielding DeltaH and DeltaS values. These values are, in turn, compared with the true values used to generate the calculated mass spectra. The results show that the reaction entropy difference between sample and reference has a very large influence on kinetic method plots. This should always be considered when studying energy-dependent mass spectra (using metastable ions or low- or high-energy collision-induced dissociation (CID)), even if only DeltaH is to be determined. Kinetic method plots are not strictly linear and this becomes a serious issue in the case of small molecules showing a large entropy effect. In such cases, results obtained at a low degree of excitation are more accurate. Energy and entropy effects can be evaluated in a relatively straightforward manner: first, the apparent Gibbs energy (DeltaG(app)) and effective temperature (T(eff)) are determined from kinetic method plots (intercept and slope, respectively), obtained from experiments using various degrees of excitation. Second, the resulting DeltaG(app) is plotted against T(eff), the slope yielding DeltaS while the intercept (extrapolation to zero temperature) yields DeltaH. This data evaluation yields more accurate results than alternative methods used in the literature. The resulting DeltaH values are fairly accurate, with errors, in most cases, <4 kJ mol(-1). On the other hand, DeltaS is systematically underestimated by 20-40%. Empirically scaling DeltaS values determined by the kinetic method by 1.35 results in a DeltaS value within 20% (or 10 J mol(-1) K(-1)) of the theoretical value.

Hydrophobic films from maize bran hemicelluloses

The covalent binding of laurylamine chains to maize bran heteroxylan (HX) was studied in order to produce hydrophobic plastic films. The process was carried out using periodic oxidation followed by reductive amination, both steps conducted in water. A kinetic study of the first step was performed, measuring periodate consumption, formic acid release and aldehyde formation. The over-oxidation effect was evaluated. The degree of substitution (DS) of dodecylamino-grafted-heteroxylan films ranged between 0.5 and 1.1 and varied as a function of experimental conditions. The maximal DS was reached under the following experimental conditions: NaIO 4 2 eq per sugar unit, laurylamine 1.7 eq, NaBH 3CN 5.8 eq per aldehyde. The plastic behaviour at room temperature was correlated to the glass transition temperature. Mechanical properties in function of the DS and the mode of obtention (casting, tape casting) were evaluated by tensile tests.

Low pressure CVD of transparent Cu-Al-O and Cu-Ti-O thin films

Semiconducting materials with optical transparency are gaining increasing attention for the preparation of next-generation optical devices. In this work, Chemical Vapour Deposition of nanophasic Cu-Ti-O and Cu-Al-O thin films is performed on glassy substrates by using copper(II) acetylacetonate hydrate [Cu(acac) 2 -H 2 O], titanium tetraisopropoxide [Ti(O 1 Pr) 4 ] and aluminium dimethylisopropoxide [(CH 3 ) 2 Al(O 1 C 3 H 7 )] as Cu, Ti and Al precursors respectively, in the temperature range 215-370°. The syntheses are carried out in a N 2 +O 2 or N 2 +H 2 O atmosphere. The obtained coatings are characterised in detail in their composition, microstructure, optical and electrical properties. The discussion is focused on the most relevant results concerning their composition, with particular attention to Cu oxidation state as a function of experimental conditions, optical transparency and semiconductor behaviour.

The cathodic reduction of activated olefins. Experimental conditions allowing the specific hydrogenation of the enone derived from ergosterol

The reduction of the bulky enone 1 derived from ergosterol was performed in non-aqueous media without and with proton donor. A fairly stable anion radical was obtained and characterized. When 1 was reduced in the presence of an efficient proton donor (benzoic acid, trifluoroacetic acid) saturation of the double bond was achieved with reasonable yield. The overall process as a function of experimental conditions is discussed.

Experimental study of Cr incorporation in pargasite

Pargasite compositions corresponding to the nominal structural formula NaCa 2 (Mg 4 Al 1-x Cr x )(Si 6 Al 2 )O 22 (OH) 2 , with O ≤ x ≤ 1, were investigated at 900 °C and 3 and 20 kbar P H₂O . The aims of this work were to determine the extent of the solid solution, i.e., the maximum x value, as a function of experimental conditions, and to characterize the M 3+ (Al 3+ and/or Cr 3+ ) distribution over the M sites. A first series of experiments at 900 ºC and 3 kbar showed the presence of large amounts of Cr 6+ as sodium chromate (Na 2 CrO 4 ) and dichromate (Na 2 Cr 2 O 7 ) in the final fluid phase, which promotes the extraction of Cr from the bulk solid (up to 45 mol%). The oxidizing agent was the oxygen from water, liberated by diffusion of hydrogen from water through the Pt tube wall. To prevent this oxidation, a new double-chamber tube was designed, one chamber contain mg powdered metallic Cr to trap the excess of oxygen and the second chamber initially containing the starting gel and water. Using this tube, (chroimum)-pargasites were produced with a maximum Cr content around 0.43 apfu from EMP analyses (based on 23 O atoms), close to the maximum Cr solubility observed in naturally occurring pargasites. In FTIR spectra of Cr-free pargasite, two intense OH-stretching bands are observed at 3714 and 3681 cm -1 , corresponding to OH groups adjacent to Mg 3 and to Mg 2 Al, respectively, and pointing toward a filled A-site. A third band is observed at 3656 cm -1 , which can be assigned to OH groups pointing toward vacant A-sites. Along the Al-Cr pargasite join, sig­nificant modifications are observed in the OH-stretching region: a new band appears at 3660 cm -1 , which can be assigned to OH groups adjacent to Mg 2 Cr, and pointing toward a filled A-site. Its relative intensity increases regularly with the Cr content, showing that Cr 3+ enters M site(s) adjacent to an OH group. Combining EMP and FTIR data, we conclude that up to 0.27 Cr per formula unit occupies the M3 site. However, these are more octahedral trivalent cations than expected, and these are balanced by lower tetrahedral Al and lower occupancies of the A and M4 sites. This charge arrangement, with important deviations from ideal stoichiometry, is apparently the only stable one under the conditions applied. Results were confirmed at 900 °C and 20 kbar P H₂O , indicating that increasing pressure does not affect Cr solubility in pargasite.

Nano-diamond films deposited by direct current glow discharge assisted chemical vapor deposition

Continuous carbon films are deposited by the direct current (DC) glow discharge assisted chemical vapor deposition method using a hydrogen–methane gas mixture. As a result of the DC-glow discharge–surface interaction, the substrate is covered by a film whose properties are strongly affected by the glow discharge and substrate conditions. It was found that under appropriate combination of the experimental parameters, a nano-sized carbon composite film containing a predominating diamond phase can be produced. The properties of the deposited carbon films were studied as a function of experimental conditions by a number of complementary techniques. The composition of the films was assessed by electron spectroscopy and the elastic recoil detection method; the morphology and structure of the films were investigated by high-resolution scanning and transmission electron microscopy (HR TEM and HR SEM). Particular attention was paid to the studies of chemical bonding of the deposited materials. For this purpose, the near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy and electron energy loss spectroscopy (EELS) techniques were used. The average film density was measured by Rutherford backscattering spectrometry. Electron diffraction, NEXAFS and EELS measurements render unambiguous evidence of diamond phase formation by the DC-glow discharge process. The nano-size dimensions of the deposited material were determined from both HR-SEM and -TEM measurements. The critical role of substrate temperature for the formation of nano-diamond particles was established based on the spectroscopic and microscopic results. Hydrogen adsorption/desorption appears to be a critical factor in this process.

Column experimental design requirements for estimating model parameters from temporal moments under nonequilibrium conditions

Data truncation is a practical necessity of laboratory column experiments because of both time and detection-limit constraints. In this paper, we study the extent to which data truncation can affect estimates of transport modeling parameters, as derived from temporal moment calculations and in the context of solute transport experiments that are influenced by sorption and nonequilibrium partitioning among mobile and immobile phases. Our results show that, for a given amount of solute used, step changes in input conditions can give more accurate moment-derived parameters than Dirac or square-wave pulses, whereas Dirac and square-wave pulses are essentially identical in terms of accuracy of parameter estimates. By simulating data truncation for a wide range of column input and transport conditions, we provide guidance toward the experimental designs that are needed to keep parameter estimation error within specified bounds, assuming nonequilibrium conditions of transport that result from either first-order or diffusion-based rate processes. More specifically, we investigate the relationships between mass of solute added to the system, minimum solute quantification limits, experiment duration times, and accuracy of parameter estimation, all as a function of experimental conditions.